Auth Operations

Comprehensive authentication and authorization patterns for secure application development across languages and frameworks.

Authentication Method Decision Tree

Use this tree to select the right authentication strategy for your use case.

What are you building?
│
├─ Traditional web application (server-rendered)?
│  └─ Session-based authentication
│     ├─ Server stores session data (Redis/DB)
│     ├─ Session ID in httpOnly cookie
│     └─ Best for: monoliths, SSR apps, admin panels
│
├─ API consumed by multiple clients?
│  └─ JWT (JSON Web Tokens)
│     ├─ Stateless, self-contained tokens
│     ├─ Access token (short-lived) + refresh token (long-lived)
│     └─ Best for: microservices, mobile apps, SPAs via BFF
│
├─ Service-to-service communication?
│  └─ API keys or Client Credentials (OAuth2)
│     ├─ API keys: simple, scoped, rotatable
│     ├─ Client Credentials: OAuth2 standard, token-based
│     └─ Best for: internal services, third-party integrations
│
├─ Third-party login (Google, GitHub, etc.)?
│  └─ OAuth2 / OpenID Connect
│     ├─ Authorization Code + PKCE for web/mobile
│     ├─ Delegate identity to trusted providers
│     └─ Best for: consumer apps, social login
│
└─ Passwordless authentication?
   └─ Passkeys (WebAuthn) or Magic Links
      ├─ Passkeys: phishing-resistant, biometric/hardware
      ├─ Magic links: email-based, time-limited
      └─ Best for: high-security, modern UX

JWT Quick Reference

Structure

Header.Payload.Signature

Header:  { "alg": "RS256", "typ": "JWT" }
Payload: { "iss": "auth.example.com", "sub": "user_123", ... }
Signature: RSASHA256(base64(header) + "." + base64(payload), privateKey)

Common Claims

Claim	Name	Purpose	Example
iss	Issuer	Who issued the token	"auth.example.com"
sub	Subject	Who the token represents	"user_123"
exp	Expiration	When the token expires	1700000000 (Unix timestamp)
iat	Issued At	When the token was created	1699999100
aud	Audience	Intended recipient(s)	"api.example.com"
jti	JWT ID	Unique token identifier	"a1b2c3d4" (for revocation)
nbf	Not Before	Token not valid before this time	1699999100

Signing Algorithms

Algorithm	Type	Key	Use When
RS256	Asymmetric (RSA)	Public/private key pair	Distributed systems, multiple verifiers
ES256	Asymmetric (ECDSA)	Public/private key pair	Same as RS256, smaller keys/signatures
HS256	Symmetric (HMAC)	Shared secret	Single service, simple setups

Rule of thumb: Use asymmetric (RS256/ES256) when the token issuer and verifier are different services. Use HS256 only when a single service both creates and verifies tokens.

Access + Refresh Token Pattern

┌──────────┐                    ┌──────────┐
│  Client   │─── login ────────>│  Auth    │
│           │<── access (15m) ──│  Server  │
│           │<── refresh (7d) ──│          │
│           │                   └──────────┘
│           │─── API call ─────>┌──────────┐
│           │    (access token) │ Resource │
│           │<── response ──────│  Server  │
│           │                   └──────────┘
│           │─── access expired │          │
│           │─── refresh ──────>│  Auth    │
│           │<── new access ────│  Server  │
│           │<── new refresh ───│  (rotate)│
└──────────┘                    └──────────┘

• Access token: Short-lived (5-15 minutes), used for API calls
• Refresh token: Long-lived (7-30 days), used to get new access tokens
• Rotation: Issue a new refresh token with each use, invalidate the old one
• Family detection: Track refresh token lineage; if a revoked token is reused, invalidate the entire family

OAuth2 Flow Decision Tree

What type of client?
│
├─ Web app with backend (Next.js, Rails, Django)?
│  └─ Authorization Code + PKCE
│     ├─ Redirect user to authorization server
│     ├─ Receive code at callback URL
│     ├─ Exchange code for tokens server-side
│     └─ PKCE prevents code interception attacks
│
├─ SPA (React, Vue) without backend?
│  └─ Authorization Code + PKCE (via BFF)
│     ├─ Use a Backend-for-Frontend to handle tokens
│     ├─ Never store tokens in browser-accessible storage
│     └─ BFF proxies API calls with token attached
│
├─ Mobile app (iOS, Android)?
│  └─ Authorization Code + PKCE
│     ├─ Use custom URI scheme or universal links for redirect
│     ├─ PKCE is mandatory (public client)
│     └─ Store tokens in secure enclave/keystore
│
├─ Server-to-server (no user)?
│  └─ Client Credentials
│     ├─ Authenticate with client_id + client_secret
│     ├─ No user context, service-level access
│     └─ Token cached until expiry
│
├─ CLI tool or smart TV?
│  └─ Device Code
│     ├─ Display code and URL to user
│     ├─ User authenticates on another device
│     ├─ CLI/TV polls for completion
│     └─ Good UX for input-constrained devices
│
└─ Microservice acting on behalf of a user?
   └─ Token Exchange (RFC 8693)
      ├─ Exchange user's token for a scoped downstream token
      ├─ Maintains user context across services
      └─ Use `act` claim for delegation chain

Authorization Model Decision Tree

How complex are your access control needs?
│
├─ Simple: just "can user X do action Y"?
│  └─ Permission-based (direct)
│     ├─ user_permissions table
│     ├─ Simple to implement, hard to scale
│     └─ Good for: small apps, prototypes
│
├─ Users grouped into roles with fixed permissions?
│  └─ RBAC (Role-Based Access Control)
│     ├─ Roles: admin, editor, viewer
│     ├─ Each role has a set of permissions
│     ├─ Users assigned one or more roles
│     └─ Good for: most apps, admin panels, team tools
│
├─ Decisions depend on attributes (time, location, resource owner)?
│  └─ ABAC (Attribute-Based Access Control)
│     ├─ Policies evaluate subject + resource + environment attributes
│     ├─ "Allow if user.department == resource.department AND time < 17:00"
│     ├─ Flexible but complex
│     └─ Good for: enterprise, compliance-heavy, context-dependent access
│
└─ Access based on relationships (owner, parent, shared with)?
   └─ ReBAC (Relationship-Based Access Control)
      ├─ Google Zanzibar model
      ├─ Tuples: user:alice#viewer@document:report
      ├─ Supports inheritance: folder viewer → document viewer
      ├─ Tools: OpenFGA, SpiceDB, Ory Keto
      └─ Good for: file sharing, nested resources, social features

Session Management Quick Reference

Cookie Security Settings

Setting	Value	Purpose
SameSite	Strict	Cookie sent only for same-site requests (best CSRF protection)
SameSite	Lax	Cookie sent for top-level navigations (good default)
SameSite	None	Cookie sent for cross-site requests (requires Secure)
Secure	true	Cookie only sent over HTTPS
HttpOnly	true	Cookie not accessible via JavaScript (prevents XSS theft)
__Host- prefix	N/A	Requires Secure, no Domain, Path=/ (strictest)
__Secure- prefix	N/A	Requires Secure flag
Max-Age	seconds	Cookie lifetime (prefer over Expires)
Path	/	Scope cookie to path (usually /)

Recommended Cookie Configuration

Set-Cookie: __Host-session=abc123;
  Secure;
  HttpOnly;
  SameSite=Lax;
  Max-Age=86400;
  Path=/

Session Expiry Strategies

Strategy	Typical Value	Notes
Idle timeout	15-30 minutes	Reset on each request
Absolute timeout	8-24 hours	Force re-authentication
Sliding window	30 min idle, 8h max	Best balance
Remember me	30 days	Extended session, reduced privileges

Password Handling Quick Reference

Hashing Algorithms

Algorithm	Verdict	Notes
argon2id	BEST	Memory-hard, resists GPU attacks, recommended by OWASP
bcrypt	GOOD	Battle-tested, cost factor 12+, 72-byte input limit
scrypt	GOOD	Memory-hard, less common library support
PBKDF2	ACCEPTABLE	FIPS compliant, use 600k+ iterations with SHA-256
SHA-256/512	BAD	Too fast, no salt built-in, easily brute-forced
MD5	NEVER	Broken, rainbow tables widely available

Password Rules (NIST 800-63B)

Rule	Guidance
Minimum length	8 characters (12+ recommended)
Maximum length	At least 64 characters
Complexity rules	Do NOT require special chars/uppercase/numbers
Breached password check	Check against known breached passwords (HaveIBeenPwned API)
Password hints	Do NOT allow
Forced rotation	Do NOT force periodic changes (only on breach)
Paste into password field	ALLOW (supports password managers)

Rate Limiting Login Attempts

Attempt	Response
1-5	Normal login
6-10	CAPTCHA required
11-20	Progressive delays (2s, 4s, 8s...)
20+	Temporary account lockout (15-30 min)

Important: Use consistent response times for both success and failure to prevent timing-based username enumeration.

MFA Quick Reference

Methods Ranked by Security

Method	Security	UX	Notes
WebAuthn/Passkeys	Highest	Good	Phishing-resistant, hardware-backed
TOTP (Authenticator)	High	Medium	App-based (Google/Microsoft Authenticator)
Push notifications	High	Good	Requires mobile app
Email OTP	Medium	Medium	Depends on email security
SMS OTP	Low	Easy	SIM swap vulnerable, use as fallback only

TOTP Implementation Checklist

• Generate 160-bit secret (base32 encoded)
• Build otpauth:// URI with issuer and account
• Display QR code for authenticator scanning
• Require verification of first code before enabling
• Accept current window +/- 1 (30-second steps)
• Generate 8-10 single-use backup codes
• Hash backup codes before storing
• Allow recovery via verified identity

Passkey/WebAuthn Checklist

• Generate cryptographic challenge on server
• Set relying party ID (your domain)
• Store credential public key and ID
• Verify signature on authentication
• Support multiple credentials per user
• Handle platform vs cross-platform authenticators
• Provide fallback auth method

Common Gotchas

Gotcha	Why It's Dangerous	Fix
JWT stored in localStorage	XSS can steal tokens, no expiry enforcement by browser	Use httpOnly cookies or BFF pattern
Missing PKCE in OAuth2	Authorization code interception attacks possible	Always use PKCE, even for confidential clients
Role explosion in RBAC	Hundreds of roles become unmanageable	Move to ABAC or ReBAC for complex scenarios
String comparison for tokens	Timing attacks reveal token value character by character	Use constant-time comparison (crypto.timingSafeEqual)
No token revocation strategy	Cannot invalidate compromised JWTs before expiry	Short expiry + refresh tokens, or maintain a blocklist
CORS with credentials: true	Access-Control-Allow-Origin: * does not work with credentials	Specify exact origin, set Access-Control-Allow-Credentials: true
SameSite=None without Secure	Browser silently rejects the cookie	Always pair SameSite=None with Secure flag
Refresh token reuse without detection	Stolen refresh tokens grant indefinite access	Rotate refresh tokens, detect reuse (token families)
Using OAuth2 Implicit grant	Tokens exposed in URL fragment, no refresh tokens	Use Authorization Code + PKCE instead (Implicit is deprecated)
Password in URL or logs	URLs are logged by proxies, browsers, and servers	Always send credentials in request body or headers
Missing CSRF protection with cookies	Cookie-based auth is vulnerable to cross-site request forgery	Use SameSite cookies + CSRF tokens for state-changing ops
Long-lived access tokens (hours/days)	Large attack window if token is compromised	Keep access tokens to 5-15 minutes, use refresh tokens
Storing API keys in plaintext	Database breach exposes all keys	Hash stored keys (SHA-256 of key), store prefix for lookup
Not validating JWT aud claim	Token meant for Service A accepted by Service B	Always validate aud matches your service identifier
Session fixation	Attacker sets session ID before login, then hijacks it	Regenerate session ID after authentication
Hardcoded secrets in code	Secrets leak via source control	Use environment variables or secret managers (Vault, AWS SSM)

Reference Files

File	Contents	Lines
references/jwt-sessions.md	JWT structure, signing, sessions, cookies, CSRF, storage	~650
references/oauth2-oidc.md	OAuth2 flows, OIDC, provider integration, social login	~700
references/authorization.md	RBAC, ABAC, ReBAC, RLS, multi-tenant, audit logging	~600
references/implementation.md	Password hashing, MFA, rate limiting, API keys, reset flows	~550

See Also

• security-ops - Broader security patterns: OWASP, headers, input validation, encryption
• api-design-ops - API design including authentication endpoints, rate limiting
• postgres-ops - Row-level security (RLS) policies for database authorization